Various plastic materials have been used as raw materials of bottles for drinks such as juice, natural water and tea drinks of various kinds in recent years. Among them, polyesters such as polyethylene terephthalate have widely been employed because of their excellence in transparency, gas barrier property, heat resistance and mechanical strength.
For example, the above tea drinks are sterilized by heating in advance and the hot tea drinks are charged in bottles. Therefore, the plastics for use in molding the bottles must have excellent heat resistance. Otherwise, the bottles may have the problems of deformation, shrinkage, swelling, etc.
On the other hand, carbonated beverages are first charged in bottles and then sterilized by heating. Thus, the bottles must retain excellent heat resistance even when the internal pressures thereof are high. Otherwise, the bottles may have the problems of deformation, shrinkage, swelling, etc. Therefore, there are demands for plastic bottles having properties ensuring capability of retaining self-standing property without deformation even after they are filled with a carbonated beverage, stoppered and subjected to heat sterilization (hereinafter occasionally referred to as "pressure resistant properties at high temperature").
Base-cup-equipped bottles having a base cup provided at a round bottom part thereof have been employed in such uses. However, the above base-cup-equipped bottles encounter the problems that the production cost is high and that the recycling is difficult because the bottle body is composed of a polyester while the base cup is composed of a different material such as polyethylene with the result that the attempt to melt the whole bottle and remold the melt into bottles and the like would lead to production of only items which are inferior in transparency and other properties.
In the above circumstances, the inventors have made extensive and intensive investigations with a view toward obtaining a self-standing bottle which hardly deforms at, for example, its neck/mouth part and bottom part when heat sterilization is applied to the contents filled therein and which is composed of the same material in its whole structure to enable recycling. As a result, it has been found that a bottle which is composed of a specified polyester composition and which meets given criteria at a given hot bath test can attain the above object. The present invention has been completed on the basis of the above finding.